The present invention relates generally to certain construction and construction methods for making printheads of hard-copy-producing devices such as computer printers, graphics plotters and facsimile machines. More particularly, the present invention concerns the construction of a printhead of a thermal inkjet printer that includes one or more printhead dies, each with a stepped shape, interconnected to a carrier substrate that also has a stepped shape.
Ink-jet technology is employed in hard-copy-producing devices such as computer printers, graphics plotters and facsimile machines. By way of background, a description of ink-jet technology is provided in various articles in the Hewlett-Packard Journal such as those in the following editions: Vol. 36, No. 5 (May 1985), Vol. 39, No. 4 (August 1988), Vol. 39, No. 5 (October 1988), Vol. 43, No. 4 (August 1992), Vol. 43, No. 6 (December 1992) and Vol. 5, No. 1 (February 1994).
An inkjet pen typically includes an ink reservoir and an array of inkjet printing elements, or nozzles. The array of printing elements is formed on a printhead. Each printing element includes a nozzle chamber, a firing resistor and a nozzle opening. Ink is stored in an ink reservoir and passively loaded into respective firing chambers of the printhead via an ink refill channel and ink feed channels. Capillary action moves the ink from the reservoir through the refill channel and ink feed channels into the respective firing chambers. The printing elements are formed on a common, so-called carrier substrate.
For a given printing element to eject ink a drive signal is output to that element""s firing resistor. Printer control circuitry generates control signals which in turn generate drive signals for respective firing resistors. An activated firing resistor heats the surrounding ink within the nozzle chamber causing an expanding liquid bubble to form. The bubble forces ink from the nozzle chamber out the nozzle opening. A nozzle plate adjacent the barrier layer refines the nozzle openings. The geometry of the nozzle chamber, ink feed channel and nozzle opening defines how quickly a corresponding nozzle chamber is refilled after firing. To achieve high quality printing ink drops or dots are accurately placed at desired locations for desired resolutions. It is known to print at resolutions of 300 dots per inch and 600 dots per inch. There are scanning-type inkjet pens and non-scanning type inkjet pens. A scanning-inkjet pen includes a print head having approximately 100-200 printing elements. A non-scanning type inkjet pen includes a wide-array or page-wide-array print head. That type of print head includes more than 5,000 nozzles extending across the width of a page. Nozzles for page-wide-array print heads like that are controlled to print one or more lines at a time.
In connection with forming printing elements on carrier substrates, a printhead die is connected to such a substrate. The outer surfaces of conventional printhead dies have a linear, non-stepped shape. As a result, the die is adhered in place in a recess formed in the substrate, as a block being placed in a recess. When the die and substrate are connected, the outer surface of the die adjoins the outer surface of the substrate. To make necessary electrical connection between printer-operational integrated circuits (ICs) located in the die and substrate, electrical connectors such as wire bonds or tape-automated bonding (TAB) circuit coupons are used. Those electrical connectors are placed to span the intersection of the outer faces of the die and substrate.
There are problems associated with locating the electrical connectors adjacent the outer face of the die and substrate. Those problems are associated with placing a critical component of the printhead, the electrical connectors for the die and substrate, in a location subject to attack/degradation by the printhead environment. That environment includes chemical attack on the connection via ink, and degradation due to abrasion when devices know as wipers are used during a conventional cleaning operation.
The invention is an interconnected printhead die and carrier substrate system for a printhead in hard-copy-producing devices used to print on print media and includes a printhead die and a carrier substrate. The die and the substrate are coupled and each has an operative face separated from an inner face, and includes integrated circuits formed therein. At least three spacers are positioned between the die and substrate to define a space that is filled with an adhesive/under-fill layer. An electrical-connection region is located adjacent the inner faces of the die and substrate, and is effective to accommodate bilateral communication between integrated circuits formed on the die and the substrate.
The die and the substrate may have what is characterized as a stepped shape, and a cavity is formed by the stepped die and stepped substrate, with the electrical-connection region being located in the cavity. The electrical-connection region is also encapsulated with an encapsulant that may fill the cavity. The operative face of the die is not encapsulated, and one version of the system includes having the operative faces of the die and the substrate may also be covered with a protective coating having a differentiated thickness.
The spacers may be formed integrally with the carrier substrate as a stand-off or bump extending upwardly from substrate in the range of about 3 mils (0.003 inches). At least three and preferably four bumps are formed on the carrier substrate in positions opposing the four corners of generally rectangularly shaped printhead die. Having at least three bumps defines a level plane for exact placement of the die in desired position over the substrate.
Another feature of the invention is a two-step process of coupling die 312 to substrate 314. The first step is to temporarily tack the die to the substrate by applying a suitable first adhesive to the upper ends of the bumps. A suitable curing process is performed, and the result is to precisely fix the die temporarily in a desired position. That position is 3 mils from the opposing surface of the substrate. The second step is to apply an second adhesive/under-fill material to fill in the space between the die and the substrate. The two-step die-substrate coupling process improves planarity of the die and its corresponding operative face. By following the two-step process with two different adhesives, the possibility of undesired lateral micro-movement of the die relative to the substrate is minimized.
The invention provides an interconnected system in which protection occurs in regions of the die and substrate where electrical connections are made. The stepped features of the die and substrate cause the electrical-connection region to be located inwardly of the ink-flow architecture of the printhead in a place that is protectible by encapsulants or other protective materials/mechanisms. In addition, the stepped feature die places the operative face of the die in the desired location closest to the print media.
These and additional objects and advantages of the present invention will be more readily understood after consideration of the drawings and the detailed description of the preferred embodiments which follow.